1. Field of the Invention
The present invention relates to straddle-type vehicles (for example, motorcycles), and more particularly, relates to a straddle-type vehicle equipped with an electronically controlled continuously variable transmission.
2. Description of Related Art
Straddle-type vehicles such as scooter-type motorcycles widely use a V-belt continuously variable transmission. A V-belt continuously variable transmission includes a pair of primary and secondary sheaves with variable groove widths, the primary sheave being disposed on a primary shaft to which the output of a power source such as an engine is input, and the secondary sheave being disposed on a secondary shaft which takes out the output to the driving wheel. A V-belt is wound around both sheaves, and the winding diameters of the V-belt around the sheaves are adjusted by changing the groove widths of each of the sheaves by a groove-width adjusting mechanism, so that the speed change ratio between both sheaves is controlled in a stepless manner.
The primary sheave and the secondary sheave are generally each composed of a fixed flange and a moving flange between which a V-groove is formed. Each moving flange is movable along the axis of the primary shaft or the secondary shaft. The moving flange is moved by a groove-width adjusting mechanism so that the speed change ratio can be controlled in a stepless manner.
Some conventional V-belt continuously variable transmissions of this type use an electric motor to move the moving flange of the primary sheave to adjust the groove width. This structure allows the groove width to be adjusted freely, since the moving flange can be moved in either a direction to decrease the groove width of the primary sheave (to Top), or in a direction to increase the groove width (to Low), by the moving thrust of the electric motor (for example, refer to Japanese Patent No. 3,043,061).
Scooter-type motorcycles equipped with a mechanism to electronically control a V-belt type continuously variable transmission change the speed change ratio automatically according to a program (map) input in advance for vehicle speed and engine speed (accelerator position) without the need for the operation of the rider. This provides the rider with ease of driving operability. For this reason, various attempts to apply this automatic continuously variable transmission to various types of vehicle have been made today.
Some motorcycles equipped with this type of automatic continuously variable transmission have a plurality of drive modes with different speed-change characteristics using a plurality of the above-mentioned programs (maps). For example, JP-A-7-119804 discloses a vehicle having programs (maps) for specifying a plurality of drive modes, in addition to a normal mode map for normal driving, a sports mode for frisky and agile driving and an engine braking mode for downhill runs. This vehicle allows the drive mode maps to be selected automatically according to a determination on the driving state of the vehicle (accelerator position, whether under braking or not), enabling the rider to perform accurate driving according to the driving state without any switching operation.
However, the vehicle of JP-A-7-119804 has the problem that the rider cannot switch among the maps for specifying the respective drive modes according to rider's intention because the maps are selected automatically; for example, the rider cannot accelerate freely even if the rider wants to increase speed sharply during passing or climbing a hill, or the rider cannot apply engine braking freely even if the rider wants to decrease speed before entering a curve.